[Aorai] Fix metavariable assignement typing and metavariable Cil declaration

src/plugins/aorai/aorai_utils.ml

src/plugins/aorai/data_for_aorai.ml

src/plugins/aorai/promelaast.mli

src/plugins/aorai/tests/ya/oracle/stack.res.oracle

src/plugins/aorai/tests/ya/stack.i

src/plugins/aorai/tests/ya/stack.ya

src/plugins/aorai/yaparser.mly